1. Technical Field of the Invention
The present invention relates to an electrooptic device such as a liquid crystal device and an electroluminescence (EL) device, a driving IC suitable for use in the electrooptic device, and an electronic apparatus comprising the electrooptical device.
2. Description of the Related Art
Recently, electrooptic devices such as liquid crystal devices and EL devices are widely used in electronic apparatuses such as cellular phones, portable information terminals, and personal computers. The electrooptic devices are, for example, used in display units for displaying various information about the electronic apparatuses.
Generally, the electrooptic devices such as liquid crystal devices and EL devices have a panel structure in which an electrooptic material such as liquid crystal or EL is two-dimensionally arranged on a substrate. In a panel structure of a chip-on-glass (COG) mounting type, a driving IC is directly mounted on a substrate supporting an electrooptic material. The COG-type panel structure is made by bonding active faces of the driving IC to the substrate through a conductive bonding element such as anisotropic conductive film (ACF).
The above conventional electrooptic devices often suffer from display failure when an external force is applied to the electrooptic device by dropping, for example. The inventors have conducted various experiments to find the cause of the display failure. As a result, the inventors have found that the cause of the display failure is the disconnection between the terminal of the driving IC, i.e., a bump, and the terminal on the substrate caused by local detachment of the driving IC bonded onto the substrate using ACF or the like due to the application of the external force.
To describe in detail, first, a liquid crystal device having the structure shown in FIG. 7 was prepared. This liquid crystal device was made by bonding a small glass 51 and a large glass 52 with a sealing material 53, filling the interior with liquid crystal through a liquid crystal inlet 53a provided at a portion of the sealing material 53, and mounting a driving IC 56 on an overhang section 52a of the large glass 52 with an ACF 54. Two types of the driving IC 56, i.e., one having a planar dimension A×B=9.6 mm×1.8 mm and the other having a planar dimension A×B=13.93 mm×2.1 mm were prepared so as to make two liquid crystal devices of different type.
In these two liquid crystal devices, while supporting the large glass 52, a force F of 15 Newton (N) is applied to the face of the small glass 51 having a width of 0.5 mm from an edge of the small glass 51 so that the edge of the small glass 51 is moved in the force application direction by 0.2 mm. At this time, stresses generated at each position in the region from a corner P0 at the small glass 51 side to an opposing corner P1 relative to a shorter side and stresses generated at each position in the region from the corner P0 to an opposing corner P2 relative to a longer side were measured.
The results of the measurement are shown as a graph in FIG. 8. The graph demonstrates the following:
(1) A significantly high stress is generated at the corner P0 located at the small glass 51 side of the driving IC 56 and at the vicinity thereof, readily causing the detachment of the driving IC 56;
(2) At a position 0.2 mm distant from the corner P0, the stress is sufficiently low so as not to cause problems during use; and
(3) In the vicinity of the opposing corner P1 relative to the short side, the stress increases again but not as high as that at the corner P0 at the small glass 51 side.
The present invention is made based on the above-described findings. An object of the present invention is to prevent display failure of the electrooptic device even when an external force caused by, for example, dropping, is applied to the electrooptic device such as a liquid crystal device, by improving the terminal structure, i.e., the bump structure, of IC chips such as driving IC chips.